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Multi-rate Congestion Control

Multi-rate Congestion Control. Tapan Karwa CS590F. Multi-rate Data Organization. Simulcast : Different multicast groups, each sending all the data/signal at different rates. Cumulative : Layered division of data. Each layer on a different mcast group. Higher layers refine data. Related Work.

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Multi-rate Congestion Control

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  1. Multi-rate Congestion Control Tapan Karwa CS590F

  2. Multi-rate Data Organization • Simulcast : Different multicast groups, each sending all the data/signal at different rates. • Cumulative : Layered division of data. Each layer on a different mcast group. Higher layers refine data.

  3. Related Work • RLM : • Uses a state machine. Adaptive timer controlled experiments used to decide subscription. • Shared learning. • Digital Fountain Approach : • Combine Tornado codes with layered mcast, to enable ‘digital fountain’. • Start drinking at any time and adapt drinking rate to available BW. Need any k out of (k+l)

  4. Related Work • RLC : Receiver-driven Layered CC • Congestion control is achieved using SP’s. Burst of data sent right before SP. • Receivers make join attempts only after a SP. Allows new users to quickly ramp up by placing SP’s conveniently. • BW doubles with every higher layer and number of SP’s decrease with every higher layer. • Synchronizes receivers.

  5. Technique • All these schemes wait for loss before they react. • Use ECN mechanism : • Don’t have to wait for loss to detect congestion. • No wastage of resources already used by packets. • Significance for streaming video/audio. • No loss computation at the receiver. Hence, faster. • Current routers are normally in the regime of probabilistic marking. Effect of using ECN mechanisms. • Not looked at yet!

  6. Problems to be Dealt With • How many marked packets should the receiver wait for – One or more? • TCP suggests considering a marked packet as a dropped packet and reacting accordingly. Other mcast CC schemes also wait for a single packet loss to react. • Solutions : • Wait for a single marked packet. Too aggressive in dropping especially considering probabilistic marking. • Wait for a subset proportional to data rate of highest layer. What subset? ½? Effect on TCP flows? Is this an engineering problem?

  7. Things to be Measured • Quality as indicated by Loss Rates : • Effect on TCP flows. • Convergence Time • Stability in terms of layers subscribed to.

  8. Future Avenues • Sender-based schemes using ECN information to dynamically alter sending rates. • Using Diffserv mechanisms with ECN. • Other proxy based schemes.

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